1. Field of the Invention
The present invention relates to a method of operating an internal combustion engine, especially of a motor vehicle, in which an air mass and a fuel mass are fed into a combustion chamber in a combustion cycle, wherein the mixture composition ratio (lambda) of the air mass to the fuel mass is pre-adjustable. Further it also relates to a suitable control unit for this type of internal combustion engine.
2. Prior Art
In conventional combustion engines the air mass required for combustion is fed through an intake pipe to the combustion chamber. The fuel mass required for the combustion is similarly supplied to the combustion chamber by means of a fuel pipe and suitable injection valves in these engines or with direct gasoline injection (BDE) via a fuel intermediate reservoir (fuel rail), in which the highly compressed fuel is present at about 100 bar, in modern gasoline motors or diesel engines.
In an older previously published DE application (AZ R 32348-1) of the present inventor a method and apparatus for determination of the gas fill of a combustion engine is described. The gas mixture contained in the intake pipe is composed of fresh gas and exhaust gas. A process is described in this reference for determining the fresh gas portion in the gas flowing into the combustion chamber in order correspondingly to be able to exactly measure the amount of fuel to be made available for the combustion. To solve this problem the partial pressure of the fresh gas portion in the total mass flow flowing into the combustion chamber is determined by setting up a mass balance condition and then taking the time derivative of the general gas equation. This separate balancing of the fresh gas and the exhaust gas provides the advantage that the filled fresh gas volume can be exactly determined. The subject matter of the present patent application only concerns the residual air found in the exhaust pipe because of an external exhaust gas feedback, generally not to the internal residual gas present in the combustion chamber.
In the known internal combustion engine, especially combustion engines, the air portion in the residual gas still found in the residual gas after each combustion cycle is left completely out of consideration. Furthermore it is usually assumed that no residual air will be found in the residual gas from the combustion chamber. Of course considerable errors are thus present in the stoichiometry of air and fuel taken into the combustion cycle.
Furthermore in modem combustion engines with a 3-way exhaust gas catalyzer lean operation (lamba.gtoreq.1) is basically avoided, since the nitrogen oxides (NOx) greatly increase during lean operation, which then enter the catalyzer and reduce its service life. However in contrast, the newest catalyzers also permit lean operation, since NOx fed into one of these catalyzers is reduced to N.sub.2 and O.sub.2 again by rich operation of the engine with .lambda.(lambda)&lt;1. On account of this new catalyzer engineering advance gasoline engines may now be operated like Diesel engines, which besides has considerably improved the development of the BDE combustion engines.